Manufacture of stable suspensions of coal particles



Patented Mar. 25, 1952 MANUFACTURE OF STABLE SUSPENSIONS OF COAL PARTICLES Albert Leeds Stillman, Plainfield, N. J., assignor to Fuel Research Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application August 10, 1948, Serial No. 43,546

8 Claims.

This invention relates to improvements in the production of stable suspensions and particularly to stable suspensions composed of colloidal sized solid particles and solid particles larger than colloidal size. Illustrative of the type of suspension with which this invention is concerned, are liquid fuels in which particles of coal are suspended in a fuel oil medium, such as the cracked fuel oil known to the trade as Bunker C fuel oil; paints wherein solid particles of'pigment are suspended in a drying oil, such as linseed, tung or menhaden oils; lubricants composed of oil and suspended particles of graphite; suspensions of ore particles in oil made for the purpose of smelting the ore, etc.

It is known that suspensions of the above indicated type may be made stable for relatively long periods without the use of any added stabilizing agent and without the necessity of grinding all of the particles to colloidal fineness. Many of such prior suspensions however, did not have practically unlimited or permanent stability, which is a desirable quality in the use of such suspensions. Furthermore, such prior suspensions, so far as I .am aware, were limited in the amount and size of solid particles which they could hold in permanent suspension. Thus, in such prior suspensions, a high density of solid particles was obtainable by making the average size of such particles relatively low, while suspensions containing large size particles were obtainable through the use of special liquids or solid material and with a decrease in the density of such solid material.

' It is the primary purpose of this invention to provide a suspension of the indicated type containinga relatively high density of permanently stabilized solid particles including particles of a size substantially greater than colloidal.

It is also an object of the invention to provide a process'whereby permanent stability of the solid particles is accomplished in an inexpensive manner. In accordance with the foregoing objects, I first grind the solid material as finely as possible until -from 15% .to 25% by weight of the total mass of such material has been reduced to colloidal size, namely, particle sizes less than 5000 angstroms or micron in diameter. These colloidal sized particles are then separated from the larger sized particles. This may be accomplished either by grindingthe solid material in an electric roller mill, such as in an electric roller mill known to the art as the flaymond High Side mill, and then separating out all particles less than micron in size by means of an air current, or by subjecting the solid material to the action of a steam or compressed air comminuter provided with a classifier capable of separating out the particles less than micron is size, such as a steam comminuter of the Stephanoff type.

The separated particles of less than micron size are mixed at once in a liquid medium capable of producing the phenomenon known as Brownian movement. Soon after the mixture of such colloidal sized particles in the liquid medium,' the particles will be in universal and intense erratic motion and when that condition is reached, the larger sized particles of solid material are added to the mixture. Before adding the larger sized particles, I make sure that they have been ground to a fineness such that all pass through a 200 mesh sieve. It is preferred that such larger sized particles be added to the aforesaid mixture by forced jet, in order to obtain a uniform mixture. The larger sized particles are added in suflicient amount to produce a mixture containing from 30% to by weight, of solid particles.

I have found that in order to obtain good results, it is necessary to reduce all the large size particles to less than 64 microns in diameter (approximately 230 mesh size) by subjecting such particles in the presence of the liquid medium to a grinding action. It is preferred that this be accomplished by passing the mixture through a high capacity colloidal mill such as is disclosed in United States Letters Patent No. 2,437,147 issued March 2, 1948 to Ellsworth B. A. Zwoyer.

As a result of the foregoing treatment, there will be obtained a suspension in which the solid particles completely and uniformly dispersed throughout the liquid medium, form from 30% to 60% by weight, of the mixture. None of the solid particles will exceed 64 microns in diameter, while from 15% to 25% by weight, of such particles will be colloidal in size, or less than micron in diameter. Ordinarily, the larger sized particles, above 10 microns in size, would be incapable of remaining in permanent suspension in the liquid medium, but by means of the intense Brownian movement that is set up by the particles, less than /2 micron in size, such larger particles are stabilized in the mixture. This intense and universal movement produced by 15% to 25% by weight, of the solid particles also enables me to obtain a stable suspension having the desired density of from 30% to 60% of solid particles and to maintain in permanent suspension, particles having a diameter as great as 64 microns.

The following example is given by way of illustration to afford a better understanding of the invention and to indicate results which have been obtained without limiting the invention:

Example Take 50, parts by weight, of a bituminous or semi-bituminous coal having a high grindability, namely, above 85 on the Hardgrove scale, and which ordinarily would swell when heated, such as those coals known as Pocahontas and Lower Kittaning, and grind such coal in a steam comminuter of the Stephanoff type, having a classifier set to take off all particle sizes less than A.; micron in diameter. When approximately 20% by weight, of the coal has been ground in such manner to a fineness of less than micron, such separated colloidal particles are mixed at once with 50 parts by weight, of a cracked fuel oil which has been preheated to approximately 150 degrees F. I prefer to use as the liquid medium, commercial Bunker (3 fuel oil which usually has a gravity of iE-rorn 9 to 17 B., a viscosity not greater than 300 seconds at 122 degrees F. (Saybolt furol viscosimeter), a flash point not lower than 150 degrees F. (Pensky-Martens closed tester) and water and sediment not to exceed 2%. Soon after the colloidal sized particles of coal are mixed with the fuel oil, it will be found that such particles are in intense and vigorous Brownian movement.

The unmixed 80% by weight, of the coal left from the grinding step is then screened through a sieve of 200 meshes per linear inch to make sure that it contains no particles greater than 200 mesh. These particles are then added by forced jet to the mixture containing the colloidal sized particles, resulting in a coal-oil mixture containin ,0 parts by weight, of oil and 50 parts 'by weight. of coal, the latter including approximately 20% by weight, of particles less than /2 micron in size and 80% by weight, of particles greater than micron in size. I have found that I am unable to obtain a satisfactory product by simply grinding coal to a minus 200 mesh and then homogenizing it with the oil. When however, the coal is ground in the manner aforesaid, so that at least 20% by weight of the coal is under micron in size and such colloidal sized particles are first mixed with the oil to create an intense Brownian movement of such particles before the remainder ofthe coal is intimately included in the mixture, the larger sizes of coal will be permanently stabilized in the suspension and will not settle out. I have also found that the stability of the suspension is greatly increased if thereafter, the mixture is homogenized under pressure in a mill such as the previously mentioned Zwoyer mill. As a result of this step, the percentage of particles under colloidal size, namely, under micron in size, will not be materially increased, but the larger sized particles will be reduced so that all the coal can pass through a screen of approximately 230 mesh.

The liquid fuel produced by the above described process will remain stable indefinitely and tests have shown that it retains its uniformity without any settling of the coal for over seven months. The fuel in use is highly satisfactory and may be handled by the usual oil burning equipment when heated to approximately 175 degrees F.

Iclaim:

1. The method of preparing a stable suspension of particles of coal in ,a liquid medium in which such particles ordinarily would be incapable of remaining in suspension, which comprises mixing from 15% to 25%, by weight, of such coal particles of a size not greater than onehalf a micron with a hydrocarbonaceous liquid medium capable of producing Brownian movement with such particles, and then when such movement has become sufliciently intense to sustain larger sized particles in such medium, intimately dispersing throughout the mixture particles of such coal greater than one-half micron in size and as large as but not greater than 200 mesh in size until the coal forms from 30% to 60%, by weight, of the coal liquid medium mixture.

2. The method of preparing a stable suspension of particles of coal in a liquid medium in which such particles ordinarily would be incapable of remaining in suspension, which comprises mixing from 15% to 25%, by weight, of such coal particles of a size not greater than on -half m r n wi h a hydr ca bonaceous l apa of producing Brown an movemen with such particles, and then when such movement has become sufficiently intense to sustain larger sized particles in such medium, adding to the mixture by forced jet particles of such coal greater than oneshalf micron in, size and as large as but not greater than 200 mesh in size until the coal forms from 30% to 60%. by weight, of the coal liquid medium mixture.

3. The method of preparing a stable suspension of particles of coal in a liquid medium in which such particles ordinarily would be incapable of remaining in suspension, which comprises mixing from 15% to 25%, by weight, of such coal particles of a size not greater than onehalf micron with a hydrocarbonaceous liquid medium capable of producing Brownian movement with such particles, and then when such movement has become sufiiciently intense to sustain larger sized particles in such medium, intimately dispersing throughout the mixture particles of such coal greater than one-half micron in size and as large as but not greater than 200 mesh in size until the coal forms from 30% to 60% by weight, of the coal liquid medium. mixture, and then subjecting the resulting mixture to a homogenizing action until the coal of the mixture contains no particles greater than 230 mesh size.

4. The method of preparing a stable suspension of particles of coal in a liquid medium in which such particles ordinarily would be incapable of remaining in suspension, which comprises grinding the coal until from 15% to 25%, by Weight, of such coal is reduced to particles less than one-half micron, separating such micron size particles from the, larger particles of the coal and mixing them with a hydrocarbonaceous liquid medium capable of producing Brownian movement therewith, then when such movement has become sufficiently intense to sustain larger sized particles in such medium, intimately dispersing throughout the mixture particles of such coal greater than ones-half micron in size and-as large as but not greater than 200 mesh in size until the coal forms from 30% to 60%, by Weight, of the coal-liquid medium mixture, and then subjecting the resulting mixture to a homogenizing action until the coal of the mixture contains no particles greater than 230 mesh size.

5. The method of preparing a stable dispersion of coal and fuel oil which comprises mixing 15% to 25%, by weight, of the coal finely pulverized so that it contains no particles of .a

size greater than one-half micron with a cracked fuel oil capable of producing Brownian movement with such particles, then when such movement has become sufficiently intense to sustain larger sized coal particles in the oil, dispersing throughout the mixture the remainder of the coal containing particles greater than one-half micron in size and as large as but not greater than 200 mesh in size so that the coal particles form from 30% to 60%, by weight, of the coaloil mixture, and then subjecting the resulting mixture to a homogenizing action until all of the coal particles thereof are not substantially greater than 230 mesh size. n

6. The method of preparing a stable dispersion of coal and fuel oil which comprises grinding the coal until a minor portion thereof is reduced to particles less than one-half micron in size, separating such micron size particles from the larger particles of coal and mixing them with Bunker C fuel oil which is capable of producing Brownian movement with such particles, then when such movement has become sufliciently intense intimately dispersing throughout the mixture the remainder of such ground coal particles which are small enough to pass through a 200 mesh sieve and which form the major portion of the coal in the mixture, and then subjecting the resulting mixture to a homogenizing action until the largest of the coal particles thereof are as large as but not substantially greater than 230 mesh size.

'7, A stable suspension containing particles of coal which ordinarily would be incapable of remaining in suspension therein, consisting of from to by weight, of the coal, of particles of the coal less than one-half micron in size, a hydrocarbonaceous oil capable of producin Brownian movement with such particles, and of 85% to 75%, by weight, of the coal, of particles of such coal greater than one-half micron in size and as large as but not greater than 200 mesh in size, said particles of coal forming from to by weight, of the mixture.

8. A stable suspension containing particles of coal which ordinarily would be incapable of remaining in suspension therein, consisting of from 49% to by weight, of Bunker C fuel oil, and from 60% to 30%, by weight, of ground coal particles, said coal particles containing particles as large as but not substantially greater than 230 mesh size and from 15% to 25%, by weight, of such coal particles being less than one-half micron in size.

ALBERT LEEDS STILLMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,390,228 Bates Sept. 6, 1921 2,231,513 Stillman Feb. 11, 1941 

1. THE METHOD OF PREPARING A STABLE SUSPENSION OF PARTICLES OF COAL IN A LIQUID MEDIUM IN WHICH SUCH PARTICLES ORDINARILY WOULD BE INCAPABLE OF REMAINING IN SUSPENSION, WHICH COMPRISES MIXING FROM 15% TO 25%, BE WEIGHT, OF SUCH COAL PARTICLES OF A SIZE NOT GREATER THAN ONEHALF A MICRON WITH A HYDROCARBONACEOUS LIQUID MEDIUM CAPABLE OF PRODUCING BROWNIAN MOVEMENT WITH SUCH PARTICLES, AND THEN WHEN SUCH MOVEMENT HAS BECOME SUFFICIENTLY INTENSE TO SUSTAIN LARGER SIZED PARTICLES IN SUCH MEDIUM, INTIMATELY DISPERSING THROUGHOUT THE MIXTURE PARTICLES OF SUCH COAL GREATER THAN ONE-HALF MINCRON IN SIZE AND AS LARGE AS BUT NOT GREATER THAN 200 MESH IN SIZE UNTIL THE COAL FORMS FROM 30% TO 60%, BY WEIGHT, OF THE COAL LIQUID MEDIUM MIXTURE. 